This project seeks to develop an approach to severity index construction and testing. The methods include the combining of clinical judgement and mathematical theory to produce an index that is medically appropriate and statistically sound. The joint clinical and statistical approach defines two interlocking strategies involving assessments of clinical judgement and analyses of secondary data sets. The overall objective is to develop an index that can be calibrated against the data set to which it is to be applied to establish a level of precision with respect to that data set and the dimensions it scales.